[EXP] provide signature file loading function via HTTP

[ctb]

This PR adds support for direct loading of signatures via HTTP URLs with GET, i.e the normal way of getting files from a Web server.

See discussion here, #2257.

NEXT STEPS: Per #2257, I should should look into impementing this more generically using fsspec.

So, for example, this supports:

Loading JSON sig/sig.gz files directly from Web sites

If you make raw JSON signature files available via an apache download link, you can Do Things With Them:

sourmash sig describe https://farm.cse.ucdavis.edu/~ctbrown/wort-data/wort-sra/ERR1040406.sig 

You can build manifests with HTTP URLs in them, too

For example,

sourmash sig collect https://farm.cse.ucdavis.edu/~ctbrown/wort-data/wort-sra/ERR1040406.sig -o mf.sqldb
sqlite3 mf.sqldb 'select internal_location from sourmash_sketches'

yields

https://farm.cse.ucdavis.edu/~ctbrown/wort-data/wort-sra/ERR1040406.sig
https://farm.cse.ucdavis.edu/~ctbrown/wort-data/wort-sra/ERR1040406.sig
https://farm.cse.ucdavis.edu/~ctbrown/wort-data/wort-sra/ERR1040406.sig

and then you can do things like

sourmash sig summarize mf.sqldb

In turn, this allows you to use the full machinery of picklists etc. on non-local signatures.

With the caveat that you might end up asking to download 13 TB of signature files if you make a mistake...

More on standalone manifests

So for example if you have a manifest containing a bunch of signatures you can use --include to get just the signatures containing a keyword in the name, or at a particular ksize, and build a local database just from them:

sourmash sig describe --include Sulfito farm.podar-ref.mf.csv

Summary thoughts

Anyway this is some useful mixture of oh-so-wrong and so-very-much-right...

This is probably most useful for things like genomes where the individual signatures are quite small; we could distribute just a manifest CSV file to support certain kinds of things. It's also a good reason to support better encoding formats than JSON per #1262.

NOTE: conflicts, maybe, with #1644, which also takes HTTP URLs.

Alternative/additional implementation thoughts

Instead of a custom loader fn for signatures only, we could generically support grabbing files and turning them into file handles for signature, pathlist, and manifest loading.

[codecov]

Codecov Report

Attention: Patch coverage is 33.33333% with 6 lines in your changes missing coverage. Please review.

Project coverage is 92.14%. Comparing base (2e0175a) to head (0d7e715).
Report is 562 commits behind head on latest.

Files with missing lines	Patch %	Lines
src/sourmash/sourmash_args.py	33.33%	5 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           latest    #2256      +/-   ##
==========================================
+ Coverage   84.85%   92.14%   +7.29%     
==========================================
  Files         131      100      -31     
  Lines       15664    11397    -4267     
  Branches     2249     2251       +2     
==========================================
- Hits        13291    10502    -2789     
+ Misses       2082      603    -1479     
- Partials      291      292       +1     

Flag	Coverage Δ
python	92.14% <33.33%> (-0.05%)	⬇️
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[ctb]

implemented as a plug-in here: https://github.com/sourmash-bio/sourmash_plugin_load_urls